Adult cartilage is known to have little ability for repair, due primarily to a lack of active chondrogenic progenitor cells. As a result, there are limited alternatives for the treatment of osteoarthritis, most of which are targeted at the symptoms of the disease and not at a cure. Mesenchymal stem cells and cultured pre-chondrocytes isolated from a patient have the potential to be applied to the repair of cartilage if they can be delivered to the sites where needed. It is hypothesized that pre-chondrogenic cells coated with antibodies specific for cartilage matrix could be used as a method to regenerate or repair damaged cartilage. The focus of this proposal is to develop a targeting strategy for pre-chondrocytes so that these cells can be used to repair an articular cartilage defect in vivo. To achieve this goal, MSCs and pre-chondrocytes will be coated with palmitated protein G (or A [PPG/A]) and then incubated with antibodies to type II collagen or to epitopes on aggrecan molecules. These antibodies will bind to the PPNG and their antigen binding sites will be oriented outward. These cells coated with different antibodies, alone or in combination, will be tested for their ability to bind cartilage matrix on frozen sections and on explants of rabbit articular cartilage. Pre-chondrocytes will be stained with a vital fluorescent dye, coated with targeting antibodies, added to sections or explants, washed and then observed for the presence of fluorescent cells. In vitro studies will be carried out on coated cells to confirm that the coating procedure does not significantly impede the cells ability to proliferate or to differentiate into chondrocytes. Once targeting and synthesis of cartilage matrix have been demonstrated, these targeted pre-chondrocytes will be tested for their ability to repair a standard articular cartilage defect in rabbits, in vivo. The degree of repair will be assessed by histologic examination and morphometric examination of the articular cartilage defects. Experimental groups to be tested are: (1) control untreated defects, (2) targeted cell-injected, (3) PPA/g coated, and (4) untreated cell-injected. These experiments will determine if this novel cell targeting methodology effectively directs pre-chondrocytes to cartilage matrix and whether these targeted cells can contribute to the repair of damaged cartilage. The long-term goal of these studies is to develop a treatment for osteoarthritis. [unreadable] [unreadable]